Forums is one method you can and should use.

In order to find forums you can simply google your niche keyword and add forums. That should get you plenty of results to start with

You can post on any topics, the quality of links will be the same from forums, from my experience. Do a google search for DoFollow blogs and post comments on blogs related to your topic. Make them helpful and insightful, these links do wonders for SEO. I've personally done this and dominated the search results for my terms by doing this.